1. Field of the Invention
This invention relates to apparatus that is operative for breaking and shredding waste material so as to reduce it to a form suitable for disposal in ancillary processes, or for recycling.
2. Description of the Prior Art
Shredding apparatus for various items of waste material have been available in which parallel shafts have been provided with interleaved cutting or shearing elements. The shafts have been driven in opposite directions such that the interleaved elements operate to reduce the waste material in a shearing action, much like the action of scissors. It has been proposed also to provide the shredding apparatus with screen means at the outlet side of the shafts and interleaved elements to gauge the size of the reduced material. Furthermore, it has been proposed in prior apparatus to rotate the shafts at slow speeds and either in synchronism or at different speeds.
The prior shredding apparatus has embodied fluid pressure motor means arranged in closed loop or open loop drive hook-ups. Provision has been made to detect unusual rise in fluid pressure which takes place when waste material overloads or tends to stop shaft rotation. Such detection means has been arranged to reverse the normal direction of drive of the shafts for the purpose of relieving the overloads. Reversal of rotation has been instituted after a short time from initial detection of pressure rise, and restoration of the normal drive direction has been controlled by suitable timing devices.
Shredding apparatus of the type in which parallel, counter-rotating shafts, with shredding elements are employed, is exemplified by U.S. Pat. Nos. Panning et al 3,502,276 of Mar. 24, 1970; Brewer 3,578,252 of May 11, 1971; Rossler 3,662,964 of May 16, 1972; Schweigert et al 3,664,592 of May 23, 1952; Goldhammer 3,860,180 of Jan. 14, 1975; Cunningham et al 3,868,062 of Feb. 25, 1975; Baikoff 3,991,944 of Nov. 16, 1976; and Culbertson et al 4,034,918 of July 12, 1977. The patents of Rossler and of Schweigert et al disclose fixed grates at the discharge side of comminuting apparatus.
There are problems common to the foregoing apparatus and those include systems in which there is only one way to drive the shafts for producing the desired effect of shredding waste material, and there is no provision made for turning out fine or coarse material. The prior art which is arranged to incorporate reverse rotation does so only to attempt to clear a jam condition.